Abstract: Thermal and mechanical response,stress statute,deformation and damage of pre-pulled,pre-pressed and pre twisted LY12 aluminum alloy specimens caused by irradiation of high-power CW CO2 laser beam were studied in this paper.The parameters of laser irradiation and the microstructure of laser irradiated area were analyzed for different types of pre loading and different shapes of specimens. Under the combined laser beam irradiation and mechnical pre-loading,the laser beam irradiated area on the specimen was melt and depressed,causing fracture on the border area,and finally being damaged.